linux-kernel - [PATCH AUTOSEL 6.1 8/8] NFS: Avoid flushing data while holding directory locks in nfs

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Message-Id: <20250519212255.1986527-8-sashal@kernel.org>
Date: Mon, 19 May 2025 17:22:55 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Trond Myklebust <trond.myklebust@...merspace.com>,
	Jeff Layton <jlayton@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	anna.schumaker@...app.com,
	linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.1 8/8] NFS: Avoid flushing data while holding directory locks in nfs_rename()

From: Trond Myklebust <trond.myklebust@...merspace.com>

[ Upstream commit dcd21b609d4abc7303f8683bce4f35d78d7d6830 ]

The Linux client assumes that all filehandles are non-volatile for
renames within the same directory (otherwise sillyrename cannot work).
However, the existence of the Linux 'subtree_check' export option has
meant that nfs_rename() has always assumed it needs to flush writes
before attempting to rename.

Since NFSv4 does allow the client to query whether or not the server
exhibits this behaviour, and since knfsd does actually set the
appropriate flag when 'subtree_check' is enabled on an export, it
should be OK to optimise away the write flushing behaviour in the cases
where it is clearly not needed.

Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfs/client.c           |  2 ++
 fs/nfs/dir.c              | 15 ++++++++++++++-
 include/linux/nfs_fs_sb.h | 12 +++++++++---
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index a8930e6c417fc..de4ad41b14e2a 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -1052,6 +1052,8 @@ struct nfs_server *nfs_create_server(struct fs_context *fc)
 		if (server->namelen == 0 || server->namelen > NFS2_MAXNAMLEN)
 			server->namelen = NFS2_MAXNAMLEN;
 	}
+	/* Linux 'subtree_check' borkenness mandates this setting */
+	server->fh_expire_type = NFS_FH_VOL_RENAME;
 
 	if (!(fattr->valid & NFS_ATTR_FATTR)) {
 		error = ctx->nfs_mod->rpc_ops->getattr(server, ctx->mntfh,
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 70660ff248b79..1876978107ca1 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2632,6 +2632,18 @@ nfs_unblock_rename(struct rpc_task *task, struct nfs_renamedata *data)
 	unblock_revalidate(new_dentry);
 }
 
+static bool nfs_rename_is_unsafe_cross_dir(struct dentry *old_dentry,
+					   struct dentry *new_dentry)
+{
+	struct nfs_server *server = NFS_SB(old_dentry->d_sb);
+
+	if (old_dentry->d_parent != new_dentry->d_parent)
+		return false;
+	if (server->fh_expire_type & NFS_FH_RENAME_UNSAFE)
+		return !(server->fh_expire_type & NFS_FH_NOEXPIRE_WITH_OPEN);
+	return true;
+}
+
 /*
  * RENAME
  * FIXME: Some nfsds, like the Linux user space nfsd, may generate a
@@ -2719,7 +2731,8 @@ int nfs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
 
 	}
 
-	if (S_ISREG(old_inode->i_mode))
+	if (S_ISREG(old_inode->i_mode) &&
+	    nfs_rename_is_unsafe_cross_dir(old_dentry, new_dentry))
 		nfs_sync_inode(old_inode);
 	task = nfs_async_rename(old_dir, new_dir, old_dentry, new_dentry,
 				must_unblock ? nfs_unblock_rename : NULL);
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 9ea9f9087a712..a9671f9300848 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -196,6 +196,15 @@ struct nfs_server {
 	char			*fscache_uniq;	/* Uniquifier (or NULL) */
 #endif
 
+	/* The following #defines numerically match the NFSv4 equivalents */
+#define NFS_FH_NOEXPIRE_WITH_OPEN (0x1)
+#define NFS_FH_VOLATILE_ANY (0x2)
+#define NFS_FH_VOL_MIGRATION (0x4)
+#define NFS_FH_VOL_RENAME (0x8)
+#define NFS_FH_RENAME_UNSAFE (NFS_FH_VOLATILE_ANY | NFS_FH_VOL_RENAME)
+	u32			fh_expire_type;	/* V4 bitmask representing file
+						   handle volatility type for
+						   this filesystem */
 	u32			pnfs_blksize;	/* layout_blksize attr */
 #if IS_ENABLED(CONFIG_NFS_V4)
 	u32			attr_bitmask[3];/* V4 bitmask representing the set
@@ -219,9 +228,6 @@ struct nfs_server {
 	u32			acl_bitmask;	/* V4 bitmask representing the ACEs
 						   that are supported on this
 						   filesystem */
-	u32			fh_expire_type;	/* V4 bitmask representing file
-						   handle volatility type for
-						   this filesystem */
 	struct pnfs_layoutdriver_type  *pnfs_curr_ld; /* Active layout driver */
 	struct rpc_wait_queue	roc_rpcwaitq;
 	void			*pnfs_ld_data;	/* per mount point data */
-- 
2.39.5